U.S. Pat. No. 6,901,729, is incorporated herein by reference in its entirety. This patent describes a header flotation system that is referred to as “non-independent”. U.S. Provisional Application No. 60/699,492, filed Jul. 15, 2005, is also incorporated herein by reference in its entirety.
A windrower typically consists of a self-propelled tractor or similar vehicle, and a cutting mechanism which is either towed by the tractor or carried thereby. The cutting mechanism carried by a windrower is typically referred to as a header, and is supported on the windrower by forwardly projecting arms. Briefly, the arms comprise elements of a lift and flotation mechanism or mechanisms operable for setting a height of the header above the ground or other surface over which the windrower moves, the flotation permitting the header to ride lightly up and over rises in the terrain during field operation.
Headers are typically available and a variety of configurations. Common elements of different headers include cutters operable for severing crops from the field. One typical cutting mechanism is a sickle cutter which includes a row of knives which extend across the width of the header and which are powered to move reciprocally sidewardly relative to a sidewardly extending array of fixed knives or bars, thereby effecting a cutting action. Another cutting mechanism is a disk cutter including a sidewardly extending array of rotatably driven disks having knives extending radially outwardly from the outer circumferential edges thereof, the rotation of which disks effects the cutting action. Both of these types of cutters may be provided in different overall sideward widths. A typical cutting speed for a sickle type cutter is about 1500 to 1800 strokes per minute, and the for a disk cutter, about 2200 to 3200 rpm. It is typically desirable for the cutters to operate at a constant speed, but, in operation, the cutting speed may vary as a result of changing conditions such as crop population, contact with the ground, or the like. Closed loop speed control is typically used to maintain a consistent cutting speed under varying loads and engine speed changes.
The cutters are powered using a fluid drive, such as a fluid power takeoff (PTO). A pump driven by the engine of the tractor provides pressurized fluid to the PTO system. The pump can be of a fixed displacement, or variable displacement, in the latter instance, the pressurization and direction of fluid flow, and thus the speed and direction of operation of the PTO, being controlled by solenoids. Varying electrical current signals would be utilized for operating the solenoids, for operating the cutters at the desired speed and in the desired direction. In order to achieve maximum response time from the closed loop speed control system, it is desired to eliminate the variations in offset and gain of the electrically controlled pump.
Therefore, it would be desirable to have an apparatus and method which enables calibrating PTO current values on the vehicle, taking into account associated system variances, and furthermore to do this with minimal operator intervention.